Sliding member and bearing device using the same

ABSTRACT

A sliding member of the present embodiment includes a bearing alloy layer and a coating layer provided on a sliding surface side thereof. The coating layer has a resin binder with sulfide particles dispersed therein. A covering portion is provided over specific particles and is made of metal oxide comprising the same metal element as a metal element constituting the sulfide particles. When measured by an X-ray photoelectron spectroscopy and an X-ray diffraction method, a ratio of a peak height of the metal oxide to a peak height of metal sulfide by the X-ray photoelectron spectroscopy is from 0.10 to 0.50, and a ratio of the peak height of the metal oxide to the peak height of the metal sulfide by the X-ray diffraction method is 0.10 or less.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based on and claims priority to Japanese PatentApplication No. 2018-198407, filed on Oct. 22, 2018, the entire contentof which is incorporated by reference.

FIELD OF THE INVENTION

The present invention relates to a sliding member and a bearing deviceusing this member.

BACKGROUND OF THE INVENTION

Heretofore, there has been known a sliding member provided with acoating layer including a solid lubricant on a sliding surface side of abearing alloy layer (Japanese Patent Laid-Open No. 10-037962). In such asliding member, a coefficient of friction is reduced by the solidlubricant made of, for example, metal sulfide, and anti-seizure propertyimproves. In recent years, for a crankshaft of an internal combustionengine, employment of the crankshaft made of cast iron has expanded fora purpose of cost reduction. A shaft member made of the cast iron has anadvantage of excellent workability, but has a disadvantage in that afine burr-like protrusion is easily formed during processing. Thisprotrusion damages a sliding surface of the sliding member duringsliding against the sliding member that supports the shaft member, whichcauses abnormal wear of the sliding member. Such abnormal wear may leadto wear and tear of the coating layer in an initial stage of the slidingbetween the shaft member and the sliding member and it may be difficultto maintain a desired coefficient of friction.

To solve the above problem, an object of the present invention is toprovide a sliding member in which wear and tear of a coating layer aredecreased, a coefficient of friction is maintained, and a wearresistance improves, and a bearing device in which this sliding memberis used.

SUMMARY OF THE INVENTION

To achieve the above object, according to an embodiment of the presentinvention, there is provided a sliding member comprising a bearing alloylayer, and a coating layer provided on a sliding surface side of thebearing alloy layer. This coating layer has a resin binder, sulfideparticles and a covering portion. The sulfide particles are dispersed inthe resin binder, and made of metal sulfide. The covering portion isprovided over specific particles located on the sliding surface side ofthe coating layer among the sulfide particles dispersed in the resinbinder, and is made of metal oxide comprising the same metal element asa metal element constituting the sulfide particles. Furthermore, when asurface of the coating layer on the sliding surface side is measured byan X-ray photoelectron spectroscopy and an X-ray diffraction method, aratio of a peak height of the metal oxide to a peak height of the metalsulfide by the X-ray photoelectron spectroscopy is from 0.10 to 0.50,and a ratio of the peak height of the metal oxide to the peak height ofthe metal sulfide by the X-ray diffraction method is 0.10 or less.

In this way, the specific particles located on the sliding surface sideamong the sulfide particles included in the coating layer have thecovering portion. This covering portion is made of the metal oxidecomprising the same metal element as the metal element constituting thesulfide particles. Consequently, an opposite member comes in contactwith the covering portion included in the coating layer in an initialconforming stage of sliding. This covering portion is made of hard metaloxide, and therefore grinds a sliding surface of the opposite member.That is, fine protrusions such as burrs that are present on the slidingsurface of the opposite member are removed in contact with the hardmetal oxide. Furthermore, the covering portion made of the metal oxideis removed by initial sliding against the opposite member. Therefore,the covering portion is lost, and the sulfide particles are exposed onthe sliding surface. The sulfide particles slide against the smoothenedopposite member from which the protrusions are removed. As a result,wear and tear of the coating layer are decreased. Additionally, whenconformability with the opposite member is generated by the initialsliding, both the opposite member and the sliding member do not easilydamage an opposite side of the sliding. In consequence, an oil filmhaving a uniform thickness is formed between the opposite member and thesliding member. Therefore, a coefficient of friction can be maintained,and a wear resistance can improve.

Furthermore, it is confirmed by the X-ray photoelectron spectroscopy andthe X-ray diffraction method that the covering portion made of the metaloxide is present over the specific particles located on the slidingsurface side among the sulfide particles included in the coating layer.That is, the covering portion made of the metal oxide is formed in alittle region of the sulfide particles included in the coating layer onthe sliding surface side. Consequently, due to the initialconformability with the opposite member, the covering portion removesthe protrusions of the opposite member while itself being also removed.When the initial conformability is generated, the coating layer does notdamage the opposite member, and the sulfide particles made of the metalsulfide are exposed. Therefore, the coefficient of friction can bemaintained, and the wear resistance can improve.

In the present embodiment, the metal element is at least one or moreselected from the group consisting of Mo, W, Sn, Ti and Zr.

A bearing device of another embodiment of the present inventioncomprises a shaft member having a surface roughness Rz of 0.8 μm ormore, and a sliding member that slides against the shaft member andsupports the shaft member.

Consequently, when conformability of the shaft member with the slidingmember is generated, protrusions causing wear of the sliding member areremoved, and the shaft member comes in contact with sulfide particlesfrom which a covering portion is removed. Therefore, a coefficient offriction can be maintained, and a wear resistance can improve.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view showing a sliding member according to anembodiment;

FIG. 2 is a schematic view showing a cross section of a bearing deviceto which the sliding member according to the embodiment is applied;

FIG. 3 is a schematic enlarged view of a main part of the sliding memberaccording to the embodiment;

FIG. 4 is a schematic view showing a conforming process of the slidingmember according to the embodiment with a shaft member;

FIG. 5 is a schematic diagram showing an example of an XPS analysisresult of the sliding member according to the embodiment;

FIG. 6 is a schematic diagram showing an example of an XRD analysisresult of the sliding member according to the embodiment;

FIG. 7 is a schematic diagram showing test conditions of the slidingmember according to the embodiment;

FIG. 8 is a schematic diagram showing conditions of XPS analysis of thesliding member according to the embodiment;

FIG. 9 is a schematic diagram showing conditions of XRD analysis of thesliding member according to the embodiment; and

FIG. 10 is a schematic diagram showing test results of examples andcomparative examples of the sliding member according to the embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Hereinafter, a sliding member according to an embodiment will bedescribed with reference to the drawings.

As shown in FIG. 1 and FIG. 2, a sliding member 10 according to theembodiment comprises a bearing alloy layer 11 and a coating layer 12.The sliding member 10 may be stacked on, for example, a back metal layer13. As shown in FIG. 2, the sliding member 10 constitutes a bearingdevice 15 together with a shaft member 14 that is an opposite member.The sliding member 10 slides against the shaft member 14, to therebysupport the shaft member 14. In the sliding member 10, a sliding surface16 that slides against the shaft member 14 is formed on a surface of thesliding member on a coating layer 12 side. The sliding member 10 maycomprise, for example, an unshown intermediate layer between the bearingalloy layer 11 and the back metal layer 13. The bearing alloy layer 11is made of, for example, a metal such as Al or Cu, or an Al-based orCu-based alloy. The coating layer 12 is provided on a surface of thebearing alloy layer 11. That is, the coating layer 12 is provided on thesurface of the bearing alloy layer 11 on a sliding side against theshaft member 14, and has the sliding surface 16 that slides against theshaft member 14. The coating layer 12 is provided on the bearing alloylayer 11 by applying in which a general technique such as spray coating,roll coating or transfer printing is used. A thickness of the coatinglayer 12 can be arbitrarily set, and in the present embodiment, thethickness of the coating layer 12 is set to be from about 2 μm to 30 μm.The shaft member 14 is made of, for example, cast iron, and has acomparatively rough surface with a surface roughness Rz of 0.8 μm ormore.

As shown in FIG. 3, the coating layer 12 of the sliding member 10 hassulfide particles 21 and a resin binder 22. The sulfide particles 21 aredispersed in the resin binder 22. The resin binder 22 is, for example,at least one or more selected from the group consisting of polyimideresin, polyamide-imide resin, epoxy resin, phenol resin, polyamideresin, fluorine resin and elastomer. Furthermore, the resin binder 22may be a polymer alloy. The sulfide particles 21 are made of a sulfideof a metal M. The sulfide particles 21 made of the metal sulfidefunction as a solid lubricant that lubricates a portion between thesliding member 10 and the shaft member 14 during the sliding against theshaft member 14. The metal M constituting the sulfide particles 21 is atleast one or more selected from the group consisting of Mo, W, Sn, Ti,and Zr. For example, when the metal M is Mo, the sulfide particles 21included in the coating layer 12 are made of molybdenum sulfide (MoS₂).

The coating layer 12 of the sliding member 10 may contain a solidlubricant in addition to the sulfide particles 21 made of metal sulfide.The solid lubricant is, for example, at least one or more selected fromthe group consisting of graphite, boron nitride (h-BN),polytetrafluoroethylene (PTFE), melamine cyanate, carbon fluoride,phthalocyanine, graphene nanoplatelets, fullerene, ultrahigh molecularweight polyethylene (tradename “MIPELON” manufactured by MitsuiChemicals, Inc.), and Nε-lauroyl-L-lysine (tradename “AMIHOPE”manufactured by Ajinomoto Co., Inc.).

The sliding member 10 comprises a covering portion 24. The coveringportion 24 is provided over specific particles 23 located on a slidingsurface 16 side among the sulfide particles 21 included in the coatinglayer 12. Specifically, as shown in FIG. 3, the sulfide particles 21 areincluded in a dispersed state in the resin binder 22. At this time, thesulfide particles 21 are dispersed in the resin binder 22 in a pluralityof layers from a bearing alloy layer 11 side to the sliding surface 16side of the coating layer 12. The sulfide particles 21 located in thelayer on the sliding surface 16 side among these dispersed sulfideparticles 21 are the specific particles 23. That is, the specificparticles 23 are not limited to the sulfide particles 21 exposed fromthe coating layer 12 onto the sliding surface 16. For example, when thesulfide particles are buried in the coating layer 12, but the othersulfide particles 21 are not present on the sliding surface 16 side ofthe sulfide particles themselves, the sulfide particles 21 are then thespecific particles 23. Furthermore, the specific particles 23 have thecovering portion 24 on the sliding surface 16 side. The covering portion24 is made of an oxide of the metal M. The metal M constituting theoxide that forms the covering portion 24 is the same as the metal Mconstituting the sulfide that forms the sulfide particles 21. That is,when the sulfide particles 21 are made of molybdenum sulfide (MoS₂), thecovering portion 24 is made of molybdenum oxide (MoO₃). In this manner,the specific particles 23 located on the sliding surface 16 side havethe covering portion 24 made of the oxide on the sliding surface 16side.

The oxide of the metal M that forms the covering portion 24 is harderthan the sulfide of the metal M that forms the sulfide particles 21. Asshown in FIG. 4(A), in a conforming stage that is an initial stage ofthe sliding of the sliding member 10 against the shaft member 14, theshaft member 14 comes in contact with the covering portion 24 of thespecific particles 23 included in the coating layer 12. The coveringportion 24 is a hard metal oxide as described above. Therefore, forexample, when attacking fine protrusions 25 such as burrs are generatedin the shaft member 14, as shown in FIG. 4(B) and FIG. 4(C), these fineprotrusions 25 are ground by the covering portion 24 during the slidingof the sliding member 10 against the shaft member 14. On the other hand,the covering portion 24 itself is also worn during the grinding of theprotrusions 25 in the conforming stage. Therefore, when the conformingstage is completed as shown in FIG. 4(C), the covering portion 24 isremoved, and the shaft member 14 comes in contact with the sulfideparticles 21 included in the coating layer 12. Consequently, the shaftmember 14 comes in contact with the metal sulfide constituting thesulfide particles 21, and is not attacked by the hard covering portion24. Consequently, in the conforming stage with the shaft member 14, thecovering portion 24 removes the fine protrusions 25 formed in the shaftmember 14, and the covering portion itself is also removed. As a result,after the conforming stage of the sliding member 10 against the shaftmember 14, lubrication is achieved by the sulfide particles 21 includedin the coating layer 12. Furthermore, attacks from the sliding member 10to the shaft member 14 and attacks from the shaft member 14 to thesliding member 10 are reduced, and a low coefficient of friction and ahigh wear resistance are maintained.

Next, description will be made as to specifying of the sulfide particles21 and the covering portion 24 in the coating layer 12 according to theabove configuration.

In the embodiment, an end surface of the coating layer 12, that is, thesliding surface 16 is measured by an X-ray photoelectron spectroscopyand an X-ray diffraction method. The X-ray photoelectron spectroscopy(XPS) is a type of surface analysis method also referred to as anelectron spectroscopy for chemical analysis (ESCA). In the XPS, when asurface of a solid sample is irradiated with a soft X-ray under anultrahigh vacuum, electrons bound to the surface of the sample areemitted into the vacuum due to a photoelectric effect. At this time, theX-ray with which the sample is irradiated is an MgKα ray or an AlKα ray.The electrons emitted due to the photoelectric effect arephotoelectrons. Binding energy in the emission of the photoelectrons isenergy inherent in an element. Consequently, the element can bequalitatively analyzed based on the binding energy. On the other hand, amean free path along which the photoelectrons can travel without anyobstruction such as scattering or collision has a distance of aboutseveral nanometers. Consequently, an XPS detector cannot detect thephotoelectrons that are present at deep positions of several nanometersor more from the surface of the sample. In the present embodiment, theelement is analyzed in a very shallow range, i.e., a range of severalnanometers from the surface of the sample by use of such characteristicsof the XPS.

On the other hand, in the X-ray diffraction method (XRD), when thesample is irradiated with the X-ray, there is analyzed diffraction thatoccurs as a result of scattering or interference by the X-ray withelectrons around an atom. When this diffraction is analyzed, it ispossible to identify and quantify components of the sample. Atransmission capacity, that is, a penetration depth to a substance ofthe X-ray varies with a composition of the sample or a wavelength of theX-ray, but is generally from 50 μm to 100 μm. Consequently, in the XRD,the analysis is possible in a region deeper than that of the above XPS.In the present embodiment, the element is analyzed in the range of 50 μmto 100 μm from the surface of the sample by use of such characteristicsof the XRD, the range being deeper than that of the XPS.

In the sliding member 10 of the present embodiment, when the slidingsurface 16 that is the end surface of the coating layer 12 is measuredby using such XPS and XRD as described above, the following conditionsare satisfied:

-   -   (1) as a result of the analysis by the XPS, a ratio R1 of a peak        height of the metal oxide to a peak height of the metal sulfide        is from 0.10 to 0.50; and    -   (2) as a result of the analysis by the XRD, a ratio R2 of the        peak height of the metal oxide to the peak height of the metal        sulfide is 0.10 or less.

In each of the XPS and the XRD, the sliding surface 16 that is the endsurface of the coating layer 12 in the sliding member 10 is analyzed.That is, the analysis is executed from the sliding surface 16 side ofthe sliding member 10 in each of the XPS and the XRD. Consequently, inthe XPS, a region that is very close to an outermost surface in a rangeof several nanometers from the end surface of the sliding member 10 isanalyzed. Furthermore, in the XRD, a range of 50 μm to 100 μm from theend surface of the sliding member 10 is analyzed. At this time, in theXRD, the analysis is not limited to the coating layer 12 depending onthicknesses of the coating layer 12 and the bearing alloy layer 11, andthe bearing alloy layer 11 or the back metal layer 13 may be alsoanalyzed. In this case, an absolute value of a strength of the metalsulfide or the metal oxide to be measured decreases. However, even whenthe absolute value of the strength decreases, the ratio R2 to becalculated is not influenced.

As shown in FIG. 5, a relation between the binding energy and thestrength is obtained in the analysis by the XPS. At this time, the metalsulfide and the metal oxide are different from each other in bindingenergy, and hence a peak of the strength varies. FIG. 5 shows MoS₂ as anexample of the metal sulfide and MoO₃ as an example of the metal oxide.As each of the peaks of the metal sulfide and the metal oxide, a largestmain peak or a next large sub main peak is used. For example, when thepeaks of the metal sulfide and the metal oxide are superimposed on eachother and it is difficult to separate the peaks, the peak is not limitedto the main peak, and the next large sub main peak is used. When themain peak is selected, the main peak is used for both of the metalsulfide and the metal oxide. On the other hand, when the sub main peakis selected, the sub main peak is used for both of the metal sulfide andthe metal oxide. In the present embodiment shown in FIG. 5, it isdifficult to separate the main peak of the metal oxide MoO₃, and hencethe sub main peak is used for both of the metal sulfide and the metaloxide. That is, in the present embodiment, there are used a sub mainpeak p1 of the metal sulfide and a sub main peak p2 of the metal oxideshown in FIG. 5. Thus, a ratio R1 between an obtained peak height h1 ofthe strength of the metal sulfide and an obtained peak height h2 of thestrength of the metal oxide is calculated as R1=h2/h1. The strength peakis measured several times, and obtained results are averaged tocalculate the ratio R1. In the present embodiment, the ratio R1 is in arange of 0.10 to 0.50. This indicates that a presence frequency of themetal oxide constituting the covering portion 24 is high in a range ofseveral nanometers from the outermost surface of the coating layer 12 onthe sliding surface 16 side.

In the analysis by the XRD, such a diffraction pattern as shown in FIG.6 is obtained. At this time, the metal sulfide and the metal oxide aredifferent from each other in diffraction pattern. FIG. 6 shows MoS₂ asan example of the metal sulfide and MoO₃ as an example of the metaloxide. As each of the peaks of the metal sulfide and the metal oxide, anangle corresponding to the largest strength is used according to ananalysis result of the XRD. That is, in the present embodiment, a peakp3 of the metal sulfide and a peak p4 of the metal oxide are used asshown in FIG. 6. Thus, a value R2 of a ratio between an obtained peakheight h3 of the strength of the metal sulfide and an obtained peakheight h4 of the strength of the metal oxide is calculated as R2=h4/h3.In the present embodiment, this ratio value R2 is 0.10 or less. Thisindicates that the presence frequency of the metal oxide constitutingthe covering portion 24 is low in a range of 50 μm to 100 μm from theoutermost surface of the coating layer 12 on the sliding surface 16side.

As seen from these results, in the sliding member 10 of the presentembodiment that satisfies the conditions of the ratio R1 and theconditions of the ratio R2, the covering portion 24 made of the metaloxide predominates in the specific particles 23 located close to thesliding surface 16 among the sulfide particles 21 included in thecoating layer 12, while the metal sulfide constituting the sulfideparticles 21 predominates in a region deeper than the above location.That is, it is indicated that in the sliding member 10 of the presentembodiment that satisfies the above conditions, the covering portion 24made of the metal oxide is formed in the specific particles 23 locatedclose to the sliding surface 16 among the sulfide particles 21 made ofthe metal sulfide.

Next, a manufacturing method of the sliding member 10 of the presentembodiment according to the above configuration will be described.

In the sliding member 10, as shown in FIG. 3, the coating layer 12 isprovided on the surface of the bearing alloy layer 11, that is, on thesliding surface 16 side. The bearing alloy layer 11 on the slidingsurface 16 side is degreased in a pretreatment process. The surface ofthe degreased bearing alloy layer 11 is roughened by using, for example,sand blasting, machining or a surface treatment. Thus, dirt is removedby the surface roughening. Afterward, a coating material constitutingthe coating layer 12 is applied to the surface of the bearing alloylayer 11. This coating material includes the sulfide particles 21 madeof the metal sulfide. The applied coating material forms the coatinglayer 12, for example, through drying, firing or the like. When a heattreatment is performed on the sliding member 10 on which the coatinglayer 12 is formed, an oxide constituting the covering portion 24 isgenerated in the specific particles 23 included in the coating layer 12.That is, surfaces of the specific particles 23 are oxidized by the heattreatment, and a part of the metal sulfide constituting the specificparticles 23 is oxidized into the metal oxide. In this case, for theheat treatment, for example, heating with an infrared heater, heatingwith electron beams, or heating in a drying furnace can be used.Particularly, in the present embodiment, the heating with the infraredheater is preferably used. When the heating in the drying furnace oranother general heating is used, much time is required in raising atemperature. Furthermore, a temperature of a base such as the bearingalloy layer 11 also rises. Therefore, the sulfide particles 21 includedin the coating layer 12 are heated not only on a side close to thesliding surface 16 but also at positions that are far and deep from thesliding surface 16. As a result, the sulfide particles 21 in the wholecoating layer 12 are heated, and the oxidation of the metal sulfideconstituting the sulfide particles 21 also easily proceeds. On the otherhand, when the heating with the infrared heater is used, the sulfideparticles 21 included in the coating layer 12 in a range very close tothe sliding surface 16 are momentarily heated. Consequently, when heatedwith the infrared heater, the specific particles 23 located at positionsclose to the sliding surface 16 only on the sliding surface 16 side areoxidized among the sulfide particles 21 included in the coating layer 12as in the present embodiment, thereby forming the covering portion 24.

Hereinafter, examples and comparative examples of the present embodimentwill be described.

In Example 1 to Example 4 and Comparative Example 2 to ComparativeExample 4, a coating layer 12 was formed in each sample, and the samplewas then heated with an infrared heater. In Comparative Example 1, acoating layer 12 was not heated. In the heating with the infraredheater, a temperature is raised at a constant temperature rise rate.That is, when an oxidation promotion temperature at which oxidation ofmetal sulfide is promoted is T (° C.), the temperature rise rate is setto T×2 (° C./min.). Subsequently, when a surface temperature of thesample reached a predetermined range of the oxidation promotiontemperature T of the metal sulfide, the heating of the sample stopped.In this case, the predetermined range was set to a range of 75% to 85%of the oxidation promotion temperature T. Specifically, when the surfacetemperature of the sample reached the range of 75% to 85% of theoxidation promotion temperature T, the heating of the sample stopped.The surface temperature of the sample was measured by using a contactthermometer, and directly detected with a sensor. Here, the oxidationpromotion temperature T of the sample is a temperature at which, whenpowder of metal sulfide constituting a solid lubricant is heated inatmosphere for 72 hours and is gradually cooled, 30 wt % of the wholepowder becomes an oxide. In the present embodiment, a weight ratio ofthis oxide was measured by using a carbon sulfur analysis device(EMIA-810 manufactured by HORIBA, Ltd.).

As for data prepared as described above, a ratio R1 by an XPS and aratio R2 by an XRD were calculated, and a test was conducted by usingtest conditions shown in FIG. 7, to measure a wear amount of the coatinglayer 12 and a coefficient of friction after conforming. The XPS wasperformed by using AXIS ULTRA manufactured by Kratos Co. A spot size ofan X-ray was set to 1 mm, and a neutralizing gun was set to be on.Measurement conditions of the XPS were set as shown in FIG. 8. The XRDwas performed by using RINT2200 manufactured by Rigaku Corporation.Measurement conditions of the XRD were set as shown in FIG. 9.

In Example 1 to Example 4, as shown in FIG. 10, a temperature to stopheating, a temperature rise rate and metal elements were set. In Example1 to Example 4, a wear amount and a coefficient of friction afterconforming indicated satisfactory results irrespective of the setconditions. In Example 1 to Example 4, the coefficient of frictionincreased in a conforming stage, but then decreased. Then, in Example 1to Example 4, after the conforming stage was completed, lubrication wasperformed with a solid lubricant included in the coating layer 12.Therefore, the coefficient of friction indicated a small value over along period of time.

On the other hand, Comparative Example 1 and Comparative Example 2indicated a result that a wear amount was large and a coefficient offriction after conforming was high. In Comparative Example 1, adeposited coating layer 12 was not heated. Consequently, in ComparativeExample 1, a covering portion 24 made of metal oxide was not formed.Furthermore, in Comparative Example 2, a temperature to stop heating wasset to 70% of an oxidation promotion temperature T. Therefore, it isconsidered that in Comparative Example 2, the temperature does notsufficiently rise during heating, metal sulfide is not sufficientlyoxidized, and a covering portion 24 was not sufficiently formed. Inconsequence, it is considered that in Comparative Example 1 andComparative Example 2, the coating layer 12 is worn and torn by attacksfrom a shaft member 14 after a conforming stage. It is eventuallyconsidered that in Comparative Example 1 and Comparative Example 2, thecoefficient of friction gradually increases after the conforming stage.

Furthermore, Comparative Example 3 and Comparative Example 4 indicated aresult that a wear amount of a coating layer 12 was satisfactory, and acoefficient of friction after conforming was high. Comparative Example 3is an example where a temperature to stop heating is set to 90% of anoxidation promotion temperature T, and Comparative Example 4 is anexample where the temperature to stop the heating is set to 200% of theoxidation promotion temperature T. Comparative Example 3 and ComparativeExample 4 indicates that a temperature excessively rose during theheating, and a large part of sulfide particles 21 included in a coatinglayer 12 was oxidized into metal oxide constituting a covering portion24. It is considered that when the metal oxide constituting the coveringportion 24 is excessively generated, hardness of a solid lubricantincluded in the coating layer 12 increases, and a lubricating action ofthe metal sulfide deteriorates. Consequently, in Comparative Example 3and Comparative Example 4, the coating layer 12 ground a shaft member 14in a conforming stage, and then, also had high attack property to theshaft member 14. As a result, it is considered that the coefficient offriction is not easily reduced in Comparative Example 3 and ComparativeExample 4.

It is clear from results shown in FIG. 10 that an example of the slidingmember 10 satisfying the conditions of the present embodimentcontributes to decrease of wear and reduction of a coefficient offriction after conforming.

The present invention described above is not limited to the aboveembodiment, and various embodiments can be applied without departingfrom gist of the invention.

1. A sliding member comprising: a bearing alloy layer, and a coatinglayer provided on a sliding surface side of the bearing alloy layer,wherein the coating layer has: a resin binder, sulfide particlesdispersed in the resin binder, and made of metal sulfide, and a coveringportion provided over specific particles located on the sliding surfaceside of the coating layer among the sulfide particles dispersed in theresin binder, the covering portion being made of metal oxide comprisingthe same metal element as a metal element constituting the sulfideparticles, and when a surface of the coating layer on the slidingsurface side is measured by an X-ray photoelectron spectroscopy and anX-ray diffraction method, a ratio of a peak height of the metal oxide toa peak height of the metal sulfide by the X-ray photoelectronspectroscopy is from 0.10 to 0.50, and a ratio of the peak height of themetal oxide to the peak height of the metal sulfide by the X-raydiffraction method is 0.10 or less.
 2. The sliding member according toclaim 1, wherein the metal element is at least one or more selected fromthe group consisting of Mo, W, Sn, Ti and Zr.
 3. A bearing devicecomprising: a shaft member having a surface roughness Rz of 0.8 μm ormore, and the sliding member according to claim 1 that slides againstthe shaft member, and supports the shaft member.